Reinforcing of concrete masonry structures by means of exterior application of rigid metal plates to surfaces of such structures by mechanical fastening devices is a known practice. An example of this practice is illustrated in U.S. Pat. No. 5,640,825 issued Jun. 24, 1997 to Ehsani, Mohammad R., et al. These plates are utilized to subsequently attach the ends of elongated, flexible straps of sheet-form having short, randomly oriented non-metallic fibers with the straps secured in a horizontally disposed position to the wall's surface by an adhesive epoxy that is then cured. The metal plates engage with longitudinal end portions of the straps and are mechanically secured to adjacent structure which supports the wall.
It also is a known practice to strengthen load bearing concrete floors by use of carbon fibre reinforced polymer (CFRP) strips. This is accomplished through bonding of elongated strips of CFRP to the undersurface of horizontally disposed concrete floors with these strips counteracting tensile forces. These CRFP strips may also be utilized for strengthening roof sections to better accommodate roof loading generated by wind or by accumulations of snow, or combinations of wind and snow. The CFRP strips are applied in laterally spaced parallel relationship by use of a suitable adhesive. These strips may also be applied in overlying relationship to a previously applied set but disposed in orthoganal arrangement and adhesively bonded thereto but not to the surface of the concrete structure being strengthened.
Three additional previously issued U.S. patents disclosing related subject matter were noted as a result of investigating existing reinforcing techniques utilized in strengthening concrete structures. These patents are listed as follows:
[1] U.S. Pat. No. 5,308,430 issued May 3, 1994 to Saito, Makoto, et al.; PA0 [2] U.S. Pat. No. 5,326,630 issued Jul. 5, 1994 to Saito, Makoto, et al.; and PA0 [3] U.S. Pat. No. 5,447,593 issued Sep. 5, 1995 to Tanaka, Tuneo, et al.
Each of these three patents discloses a similar structural unit which provides the tensile stress resistive component for effecting strengthening of the concrete structural element to which it is applied. They each comprise a plurality of elongated fibers disposed in parallel aligned groups embedded in an uncured matrix of thermosetting resin in a sheet-form structure. This structural sheet is applied to a surface of the structural element to be strengthened by means of a thermosetting resin adhesive. The sheets are positioned on the structural element to obtain the most effective utilization of the tensile attributes of the fibers. Along with positioning of the fiber sheets with the resin, the entire mass is subjected to of ambient room temperature or application of heat at an elevated temperature appropriate to effect curing of the matrix and adhesive resins.
Another technique previously used in effecting strengthening of walls comprises utilization of a plurality of elongated structural steel beams vertically disposed in spaced parallel relationship along the inwardly facing surface of a wall. These beams are of a size and cross-sectional configuration to have sufficient strength to counteract inward flexing of the wall that would otherwise result from any unexpected excessive increase in horizontally directed forces applied to the exterior or outwardly facing surface of the wall. Each of the beams, which may be of "I", "T", "L"-shaped angle, "C"-shaped channel or other suitable configuration, has a flat-surfaced component that is positioned in contacting engagement with the wall's surface. The upper end of each beam is mechanically secured to an overlying joist and the bottom ends are fixed to the floor which,, in a basement wall strengthening situation, is typically formed of concrete. A typical technique of securing a beam to a concrete floor comprises forming a socket in the floor for each beam, inserting the beam's lower end in a respective socket, filling the socket with concrete which is permitted to harden thereby holding the beam upright and against the wall, and then securing the upper end to a joist. This technique results in a structure that is not only objectionably intrusive into a basement's interior space but, is a costly and time consuming procedure.